The present invention relates to radio frequency power amplifiers.
Portable devices such as laptop personal computers, personal digital assistants (PDA), mobile internet devices (MID), cellular phones, and so-called smart phones with wireless data communication capability are being developed in ever increasing functions and features for convenience access to internet. Correspondingly, electrical components thereof must also decrease in size while still providing effective radio transmission performance. A major component of a wireless communication device is the power amplifiers (PA). A PA can be fabricated on a single semiconductor integrated circuit (IC) chip to provide signal amplification with substantial power. However, the substantially high transmission power associated with radio frequency (RF) communication increases the difficulty of miniaturization of the transmission components.
One significant challenge for RF power amplifiers is to provide high linearity power amplification for an increasingly large number of RF frequency bands. International Telecommunication Union, for example, defines more than a dozen RF bands, as shown in Table I for International Mobile Telecommunications (IMT) standard. Each of Band I through Band XLI listed in Table I is a pair of single uplink band and single downlink frequency band. The single RF bands shown in Table I have bandwidths between 10-75 MHz. In other words, the bandwidth of a single RF bands defined by the IMT standard is commonly less than 4% of the center frequency of the respective band. Many of the single RF bands have non-overlapping frequency ranges.
To maintain amplification linearity, conventional power amplifiers usually can only cover the frequency range of a single RF band and possibly with two overlapping single RF bands. Conventional power amplifiers in general cannot cover the frequency range of two or more non-overlapping single RF bands, as defined by IMT and other RF wireless standards such as IMT-2000, WiMax, WiBro, and WiFi. For example, the bandwidth of a conventional power amplifier may be 5% or narrower than the center frequency of a single RF band. Due to the wide frequency range of non-overlapping single RF bands as described above, multiple power amplifiers are needed to operate at different RF frequency bands such as Band XII, Band XIII, Band XIV, and Band V, as shown in Table I.
TABLE IIMT-FDD Single RF Bands for User EquipmentWirelessBandUplink Frequencies (MHz)Downlink Frequencies (MHz)I1920-19802110-2170II1850-19101930-1990III1710-17851805-1880IV1710-17552110-2155V824-849869-894VI830-840865-875VII2500-25702620-2690VIII880-915925-960IX1750-17851845-1880X1710-17702110-2170XI1428-14481476-1496XII698-716728-746XIII777-787746-756XIV788-798758-768XV1900-19202600-2620XVI2010-20252585-2600XVII704-716734-746XVIII815-830860-875XIX830-845875-890XX832-862791-821.........XL2300-24002300-2400XLI3400-36003400-3600
Since most of the wireless devices are required to operate in multiple frequency bands, multiple power amplifiers typically have to be included in a single wireless device to provide linear amplification for each of the bands the wireless device operates in. The multiple power amplifiers therefore add significant complexity and cost to conventional wireless devices.
One technique to provide broadband application is to use “distributed amplifiers”, which includes, for example, “N-gate traveling-wave amplifier”. A series of low gain broadband amplifiers are cascade connected to provide increased gain. This technique, however, has many drawbacks such as complexity, large device size, gain loss for a large number of amplifiers, and difficulty for high volume production. The approach is also expensive and is not particularly suitable for mobile applications.